Urban Light Pollution Boosts Air Pollution

Living in Manhattan, where on a good night you only see a couple stars in the sky and it's never truly dark due to light pollution, this one particularly hits home for me: BBC News reports that a new presentation at the American Geophysical Union meeting in San Francisco shows how bright city lighting makes air pollution worse. Apparently all that urban light pollution interferes with chemical reactions that normally take place at night and helps clean the air which "uses a special form of nitrogen oxide, called the nitrate radical, the break down chemicals that would otherwise go on to form the smog and ozone that can make city air such an irritant to the chest. The cleansing normally occurs in the hours of darkness because the radical is destroyed by sunlight."

The research presented shows that even though urban light pollution is 10,000 times dimmer than the light from the Sun, it still suppresses the nitrate radical, slowing down nighttime cleaning up to 7%. That's based on measurements made over Los Angeles.

As for how to prevent this, short of entirely eliminating city lighting at night (which has obvious safety implications) or using red lights (which probably won't be embraced by anyone), using lighting that concentrates light downward so that little is reflected back up into the sky would minimize the disruption to air cleaning.